Web coating refers to the process of depositing one or more materials onto a thin heat-sensitive substrate, supplied in the form of a continuous, large-quantity roll (i.e., a “web”). The web is unwound and passed through one or more stations in processing equipment, each of which deposits a material onto the web, generally under vacuum. After the web passes through all of the stations, it is rewound onto another roll and readied for further processing or shipment. One product typically manufactured by such a process is magnetic recording tape, where a polyester film is coated with ferromagnetic material.
Processing equipment used for web coating generally includes a series of web transport rollers. These rollers unwind, tension, steer, and wind the web as it travels through the processing equipment. Frictional forces at the interface between the web and a roller provide traction that causes the web to move through the equipment in the direction that the rollers establish.
FIG. 1 depicts a simplified schematic representation of an example of web processing equipment 100. Processing equipment 100 includes a source 102 of web material 104 in roll form. A pumping system 116 with a pumping port 118 helps maintain the proper pressure (e.g., vacuum) in the processing equipment 100. Also included are three material deposition stations 106, 108, 110, each of which can deposit a different material onto the web 104. As the web 104 exits the last material deposition station 110, it is rewound onto a take-up roll 112.
Generally included in each material deposition station 106, 108, 110 is a web transporting roller 114 and a steering section 200. Material is deposited on the web 104 as the web 104 travels about the web transporting roller 114. FIG. 2 shows the steering section 200 in detail. In the present example, the steering section 200 includes an entering roller 202 that receives the leading edge of the web 104. The web 104 is then received by a first guide roller 204 and a second guide roller 206. The guide rollers 204, 206 are parallel to each other. The web 104 then passes to an exit roller 208 en route to the web transporting roller 114 and then on to another material deposition station or the take-up roll 112.
One common problem with the aforementioned processing equipment 100 is a misalignment 210 between the entering roller 202 relative to the guide rollers 204, 206. An additional misalignment 212 between the exiting roller 208 and the guide rollers 204, 206 can also happen. When one or both of these conditions occur, the steering section 200 often cannot restore the proper alignment. A result of this condition is that wrinkles, or creases, or both, form in the web 104 as it travels through the processing equipment 100. The wrinkles or creases tend to accelerate degradation of the coated web product. Further, the wrinkles or creases can hamper the efficient operation of the processing equipment 100, causing downtime as an equipment operator must, for example, manually realign the web 104.
From the foregoing, it will be apparent that there is still a need for a way to control the travel of the web 104 through the processing equipment 100 in order to minimize or eliminate wrinkles, or creases, or both, with minimal or no operator intervention.